Nanoparticles are important components in the development of catalytic, sensor, aerosol, filter, biomedical, magnetic, dielectric, optical, electronic, structural, ceramic and metallurgical applications. Nanoscale metallic particles exhibit volume and surface effects which are absent in the same material with dimensions in the micron range (i.e., 0.1 micron<particle diameter<1 micron).
The use of colloidal suspensions of silver as antimicrobial agents is well known. Such use is resuming increased importance as antibiotic resistant bacteria become more prolific. Minimizing the silver particle sizes is believed to be important both from the stability of the colloidal suspension and for the efficacy against microbes.
Various processes to produce nanoparticles are known in the prior art. For example, U.S. Pat. No. 5,543,133, issued to Swanson et al., discloses a process of preparing nanoparticulate agents comprising the steps of: (i) preparing a premix of the agent and a surface modifier; and, (ii) subjecting the premix to mechanical means to reduce the particle size of the agent, the mechanical means producing shear, impact, cavitation and attrition.
Likewise, U.S. Pat. No. 5,585,020, issued to Becker et al., teaches a process of producing nanoparticles having a narrow size distribution by exposing microparticles to an energy beam such as a beam of laser light, above the ablation threshold of the microparticles.
Also, U.S. Pat. No. 5,879,750, issued to Higgins et al., teaches a process for producing inorganic nanoparticles by precipitating the inorganic nanoparticles by a precipitating agent for a microemulsion with a continuous and a non-continuous phase and concentrating the precipitated nanoparticles employing an ultrafiltration membrane.
Additionally, U.S. Pat. No. 6,540,495, issued to Markowicz et al., teaches a process for making a powder containing metallic particles comprising the steps of: (i) forming a dispersion of surfactant vesicles in the presence of catalytic metal ions; (ii) adjusting the pH to between 5.0 and 7.0; (iii) mixing the dispersion with a bath containing second metal ions; and; and, (iv) incubating the mixed dispersion at a temperature sufficient to reduce the second metal ions to metal particles having an average diameter between 1 to 100 nm.
CS Pro Systems advertises a high voltage AC processor producing nanoparticles of colloidal silver. The HVAC process is claimed to produce particle sizes between 0.002 to 0.007–9 microns by imposing an AC potential of 10,000 volts across two silver electrodes in a distilled water medium.
The production of large quantities of colloidal silver solutions required for industrial applications, such as water treatment or treatment of biological fluids, are not economical by using the electrolytic approach.
The prior art methods do not provide a simple, convenient, low-cost method for producing colloidal suspensions of electrically conductive particles. It is a hallmark of the current invention to provide such a method.